One type of touchpad operates by way of capacitance sensing utilizing capacitance sensors. The capacitance detected by a capacitance sensor changes as a function of the proximity of a conductive object to the sensor. The conductive object can be, for example, a stylus or a user's finger. In a touch-sensor device, a change in capacitance detected by each sensor in the X and Y dimensions of the sensor array due to the proximity or movement of a conductive object can be measured by a variety of methods. Regardless of the method, usually an electrical signal representative of the capacitance detected by each capacitive sensor is processed by a processing device, which in turn produces electrical or optical signals representative of the position of the conductive object in relation to the touch-sensor pad in the X and Y dimensions. A touch-sensor strip, slider, or button operates on the same capacitance-sensing principle.
A first type of touchpad is composed of a matrix of rows and columns. Within each row or column there are multiple sensor elements, however, all sensor pads within each row or column are coupled together and operate as one long sensor element. The number of touches a touchpad can detect is not the same as the resolution of the touchpad. For example, even though a touchpad may have the capability to detect two substantially simultaneous touches with an XY matrix, the touchpad cannot resolve the location of the two substantially simultaneous touches.
One way to resolve the location of a second touch is if the touches arrive sequentially in time. If both touches arrive or are detected substantially simultaneously, however, there is no way to resolve which of the two pairs of potential locations constitute “actual” touches, instead of invalid touches (e.g., “ghost” touches). Thus, the two-axis touchpads are configured to resolve only a location of a single touch. Similarly, touch screens are designed to detect the presence and location of a single touch.